Noun
The lowest member of a base when divided horizontally, or of a baseboard, pedestal, or the like.
Source: Webster's dictionary5 is a common auxiliary base, or sub-base, where 6 is 'five and one', 7 'five and two', etc. Aztec was a vigesimal (base-20) system with sub-base 5. 6: senary main The Morehead-Maro languages of Southern New Guinea are examples of the rare base 6 system. Source: Internet
Therefore, the sub-base did not have to be a self-supporting structure. Source: Internet
The upper running surface provided a smooth surface for vehicles, while protecting the large stones of the sub-base. Source: Internet